Electrostatic spray device and coating system



Nov. 21, 1961 J. w. JUVINALL ELECTROSTATIC SPRAY DEVICE AND COATING SYSTEM 2 Sheets-Sheet 1 Original Filed Sept. 29, 195] .llllllllullluur INVENTOR.

JAMES W. JUVINALL A I/orney Nov. 21, 1961 J. w. JUVlNALL 3,009,442

ELECTROSTATIC SPRAY DEVICE AND COATING SYSTEM 2 Sheets-Sheet 2 Original Filed Sept. 29, 195] 'INVENTOR.

JAMES W. JUVINALL Fig.2

A flomey United States Patent Ofiice 3,009,442 Patented Nov. 21, 196.1

3,009,442 ELECTROSTATIC SPRAY DEVICE AND COATING SYSTEM James W. Juvinall, Indianapolis, Ind., assignor to Ransburg Electra-Coating Corp., Indianapolis, Ind., a corporation of Indiana Continuation of application Ser. No. 248,907, Sept. 29, 1951. 6This application Mar. 10, 1958, Ser. No.

6 Claims. (Cl. 118-626) This invention relates generally to pumping systems and more particularly it relates to pumping systems adapted to draw fluid from a single source of fluid and distribute it through a plurality of outlets.

According to conventional practice in the coating art, coating material such, for example, as paint, varnish, lacquer and enamels have been distributed from a unitary source of supply through a plurality of independent spray guns, or other applying apparatus by providing a single container or tank adapted to contain a supply of the coating fluid, applying pressure to the fluid by maintaining a given air pressure in the tank above the fluid, and distributing the fluid through a plurality of individual pipes or conduits to the spraying or coating apparatus. In these systems pressure within the distribution pipes or conduits is derived solely from the single source of air pressure within the tank.

Coating systems of this type have been adapted to mass production methods, whereby a battery of stationary spraying or atomizing devices is arranged to coat manufactured products as they are conveyed or moved past the Sprayers. It is necessary so to arrange the spraying apparatus and so to control the pressure and rate of flow of coating material, that each manufactured product Will receive a uniform coating of paint or other coating material. Conventional fluid distribution systems do not meet these requirements because it is extremely diflicult to maintain the air pressure in the paint tank at a constant value. The variation of the air pressure in the paint tank results in the variation of the fluid delivery which in turn results in nonuniform coating. Also a partial stoppage in any one of the distribution conduits will result in a decreased fluid.

delivery to that particular spraying device associated therewith, even though the air pressure at the source remains constant. Furthermore, if a particular spraying device is at a greater elevation than the other spraying, devices, there is increased hydrostatic pressure and a lower rate of fluid delivery with relation to the fixed air'pressure in the tank. A further'difiiculty arises due to the fact. that distribution of the coating material may vary with viscosity of the coating material, and hence changes of ambient.

temperature may change the rate of fluid delivery to the spraying apparatus.

In coating systems comprising electrostatic atomizers, the attainment of consistent results requires that fluid delivery to the fixed electrostatic atomizers. be constant. Because the total quantity of fluid. delivered to. electrostatic atomizers is relatively small, even small variations in quantity are to be avoided. Also, it is characteristic of such systems that a number of electrostatic atomizers are used simultaneously to provide interlaced patterns of atomized coating materials. In such systems, it becomes more, imperative that the relative rate of deliveryof fluid to the several atomizers shall remain constant. thereby to provide a coating of. uniform thickness so as to avoid a striping eifect on the finished product,

So-called' electrostatic coating systems using electrostatic atomizers also require. that the electrostatic atomizingheads or. guns be electrically isolated from ground, However, this becomes. difficult where the coating material is.

electrically conductive because the material itself may serve as an electrical conductor between the atomizing head and the grounded fluid supply system. Thus, in a conventional electrostatic coating system, conductive coat ing materials short-circuit the atomizing heads to ground through the pumping unit and it is not feasible to use such coating materials.

The principal object of this invention is to provide, in a pumping system for delivering fluid material from a source of supply to a plurality of utilization devices, apparatus for delivering fluid to each device at a constant volume rate.

A further objectof this invention is to provide, in a pumping system adapted to deliver fluid from a source of supply to a plurality of utilization devices, a plurality of pumps, each of which is connected between the source of supply and a utilization device, together with a means for driving said pumps at constant speed relative to one another.

Still another object of this invention is to provide, in a pumping system adapted to distribute fluid from a source of supply to a plurality of utilization devices, a plurality of pumps together with means for driving the pumps at variable speeds and means for maintaining a constant speed ratio between individual pumps.

A further object of this invention is to provide, in an electrostatic coating system, a pumping unit adapted to handle electrically conductive coating materials without in any way impairing the electrical operation of the system.

In accordance with this invention there is provided a pumping system adapted to draw fluid from a source of fluid and distribute it at a constant volume rate to a plurality of utilization devices comprising a group of pumps and a drive mechanism connected to each of the pumps for driving them at constant speed relative to one another.

In accordance with another feature of this invention there is provided a pumping system for electrostatic coating systems comprising a pumping unit having electrical characteristics such that electrically conductive coating material will not in any way impair the operation of the coating system.

For a better understanding of the invention, together with other and further objects thereof, reference is made to the following description, taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

In the accompanying drawings:

FIG. 1 is an isometric view illustrating a pumping unit constructed in accordance with this invention.

FIG. 2 is an isometric view illustrating a modification of the unit illustrated in FIG. 1.

FIG. 3 is a diagrammatic view of an electrostatic coating system utilizing apparatus in accordance with my invention.

In accordance with. this invention there is provided a pumping unit comprising a base plate 1 on which are mounted a drive motor 2, an infinitely variable, positive speed: reducing mechanism 3 and six positive displacement gear type fluid pumps 4. The speedv reducing mechanism is designed. to have complete reproducibility and positivelinkage between input and output speeds at all settings throughout the range of its variations. Each of the pumps 4. may be designed to have, at a given speed, the same volume rate of fluid delivery and may further be designed so that its delivery will vary directly with its speed of operation. Since this particular pump unit is especially adapted for supp-lying paint to a battery of electrosatic atomizing heads, it is sometimes desirable to spray a. greater volumeof paint from one head than from another. For example, it has been found desirable in electrostatic atomizers which include a plurality of atomizing heads under certain conditions to deliver liquid to the atomizing heads in such proportions that one-third to two-thirds more liquid is delivered to one-third of the atomizing head than to the remainder of the atomizing heads. Hence, it may be desirable to operate one or more of the pumps 4 at a different speed thereby to supply the paint to a particular head at a different rate.

The electric motor 2 may be arranged to drive input gear 5 of the speed reducer either directly or by means of an idler gear. The speed reducer 3 includes an output gear 6 for driving the idler gears 7 and 8 which in turn mesh with the gear 9. Gears 7 and 8 may be mounted in suitable hearings in a bearing support block 11. Gear 9 is connected with a jack shaft 10 which is also mounted at one end in the bearing block 11. The opposite end of jack shaft 10 may be supported in the pillow block 12. Gears 8 and 9 may be mounted outboard of block 11 to provide convenient access whereby gears of different sizes may be substituted for changing the driving speed. For driving the pumps 4 there are provided gears 13, 14 and 15 mounted on the jack shaft 10. Each of the pumps 4 is adjustably mounted in ways 16 which may be an integral part of the base plate 1. Pumps 4 are provided with drive gears 17 which are adapted to mesh with the jack shaft gears 13, 14 and 15 respectively whereby each of the jack shaft gears 13, 14 and 15 drives a pair of pumps. Pumps 4 may be adjusted on the ways 16 so that the jack shaft gears mesh properly with the drive gears of the pumps.

For introducing fluids such as paint, enamel, varnish or lacquer to the pumps 4 there are provided inlet hoses or pipes 19 and 20 which may be connected to a tank or drum (not shown). Inlet hose 19 may be connected to each of the pumps aligned therewith and hose 20 may be connected to each of the three pumps aligned therewith. The outlets of the pumps 4 may be connected to hoses or pipes 21, 22, 23, 24, and 26 respectively which in turn may be connected with atomizing guns or heads for the spraying of fluid.

In operation it will be apparent from the foregoing description that motor 2 is adapted to drive speed reducer 3 which in turn rotates the gears 7, 8 and 9 together with the jack shaft 10. Jack shaft 10 in turn drives each of the pumps through the gears 13, 14, 15 and 17. By making each of the gears 13, 14 and 15 of uniform size, and each of the gears 17 also of uniform size, all of the pumps 4 may be driven at the same speed whereby the fluid output rate of all the pumps will be identical. If it is desired to vary the output rate of one pump with respect to the others the size of its drive gear 17 may be changed accordingly to provide the desired rate. However, it should be noted that any variation of speed of motor 2 produces a corresponding variation in speed in each of the pumps 4 whereby their output rates vary in unison. It will also be apparent that variation of the reduction ratio of the speed reducer 3 by means of adjustment knob 18 will result in variation of the speeds and deliveries of the pumps, but the delivery ratio between the various pumps will remain constant.

While in this embodiment of my invention toothed wheels are shown for transferring power between the motor and the pumps, it is to be understood that driving means such as friction gearing, pulley-belt combinations, etc. may also be used in some instances without departing from my invention.

In paint spraying systems utilizing electrostatic atomizing spray heads it is common practice to insulate the heads from ground and to maintain them at a high potential with respect to ground by means of a high voltage transformer. However, if the coating material delivered to the atomizing heads through the hoses 21 to 26 is elec trically conductive the atomizing heads will be grounded electrically since the fluid serves as a conductor between the heads and the pumps even though the hoses 2126 may be of insulating material. Therefore, the pumping unit shown in FIG. 1 can be used only where the coating material is an electrical insulator, or has a sufficiently high resistance to be the equivalent of an insulator. Accordingly, where the coating material is electrically conductive it becomes necessary to provide means whereby the conductive coating material will not electrically short-circuit the atomizing head to ground.

FIG. 2 of the drawings illustrates an embodiment of this invention characterized by its ability to maintain the pumping system and the fluid supply source at the same high voltage potential as that impressed on the atomizing heads. Referring to FIG. 2 the pumping unit is comprised principally of two units, a base unit 101 and a pumping unit 102. The pumping unit is supported on base 101 by means of four insulating posts 103, 104, 105 and 106. Pump unit 102 is driven by an insulating drive shaft 107 which may be made of insulating material or may include an insulating coupling (not shown) whereby the pump unit 102 is electrically isolated from the base unit 101 and ground. A drive motor 108 may be mounted on base 101 for driving a positive, infinitely variable, speed reducer 109 which in turn operates a rightangle gear box (not shown) for driving the insulating shaft 107. Shaft 107 extends from base unit 101 to the insulated pump unit 102 where it drives a right-angle gear box 110 which in turn drives the jack shaft 111 in the same manner as described in connection with jack shaft 10 of FIG. 1. Pump unit 102 is otherwise identical to that shown in FIG. 1 and operates in precisely the same manner.

FIG. 3 of the drawings illustrates an embodiment of my invention, generally similar to that shown in FIG. 2, utilized in an electrostatic coating system. In FIG. 3 a pumping unit is supported on a base 201 and on a plate 202, which plate is supported on a plurality of insulating posts 203. Pumps 204, 205 and 206 mounted on plate 202 are driven in positive coordination and at predetermined deliveries by suitable gearing from motor 208 through variable speed reducer 209 and gear boxes 210 and 210a. Gear box 210a is electrically insulated from gear box 210 (which is at ground) by a drive shaft 211 made of suitable insulating material. Electrically conductive liquid coating material in supply source 212 is insulated from ground by columns 214 of insulating material.

On operation of the pumping unit electrically conductive coating material is drawn from supply source 212 and distributed to pumps 204, 205, and 206 from each of which the coating material is pumped at a positively controlled unvarying rate to each of the three electrostatic atomizing heads 216. Atomizing heads 216 are maintained at a high electrical potential by connection to one terminal of a high voltage source 218, the other terminal of which is connected to ground as shown. Heads 216 are suitably arranged in coating cooperation adjacent a conveyor 220 which is connected to ground and which moves a series of supported articles 222 past atomizing heads 216. The atomized coating material issuing as a spray from heads 216 is attracted to and deposited on the articles 222 as a protective or decorative coating by the electrostatic field existing between heads 216 and the articles 222.

From the foregoing description it is apparent that pump units as shown in FIGS. 2 and 3 may be used for transferring fluid from a fluid supply source which is electrically isolated from ground to electrostatic atomizing heads which are likewise electrically isolated from ground. Thus, the entire system of heads, pump and supply source can then be maintained at a high potential relative to ground even though the coating material is electrically conductive. It is also apparent from the foregoing description that, by providing a pump unit consisting of individual pumps adapted to be connected to individual atomizer heads and by driving the pumps through an infinitely variable speed reducing mechanism and a positive linkage, such as a gear train, the amount of coating material transferred from the source to the atomizing heads can be varied as desired over wide ranges and can be held constant at any value within this range. It is further apparent that the rate of delivery to any one of the six atomizing heads can be maintained in constant relationship to the rate of delivery to each of the other atomizing heads. At the same time the absolute value of rate of delivery to all atomizing heads may be raised or lowered as desired. A still further advantage of this invention resides in the flexibility provided by adjustment of speed reducer 18 together with the fact that a still wider range of variation is available by changing the gears 8 and 9 which are conveniently mounted outboard of the unit for this particular purpose.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

This application is a continuation of my copending application, Serial No. 248,907, filed September 29, 1951, now abandoned.

I claim:

1. In an electrostatic coating system including a support for an article, a plurality of atomizing devices spaced from the article and electrically insulated from ground, a supply of liquid coating material for said atomizing devices, said supply being electrically insulated from ground, and means for maintaining an electrical potential difference between said atomizing devices and the coating material emanating therefrom on the one hand and the article on the other hand for electrostatic deposition of the atomized liquid coating material on the article, the combination of an electrically grounded support, a motor drive means mounted on said support, electrically insulating posts mounted on said support, a second support means mounted on said posts, a pumping unit mounted on said second support means and adapted to be connected between said liquid supply and said atomizing devices -for delivering liquid coating material to said atomizing devices for atomization therefrom, and an electrically insulating drive shaft connecting said drive means with said pumping unit for electrically insulating said pumping unit from said drive means.

2. The invention set forth in claim 1 wherein said pump unit includes a pump for each atomizing device, each of said pumps being constructed and arranged to deliver liquid coating material at a fixed predetermined rate for any given speed of operation and being connected between said liquid supply and one of said atomizing devices, and in addition a rotatable drive member connected to said shaft, and a fixed ratio driving connection between said drive member and each of said pumps.

3. In an electrostatic coating system including a support for an article, an atomizing device spaced from the article and electrical-1y insulated from ground, a supply of liquid coating material for said atomizing device, said supply being electrically insulated from ground, and means for maintaining an electrical potential difference between said atomizing device and the liquid coating material emanating therefrom on the one hand and the article on the other hand for electrostatic deposition of the atomized liquid coating material on the article, the combination of a pumping unit electrically insulated from ground and connected between said liquid supply and said atomizing device for delivering liquid coating material to said atomizing device for atomization therefrom, a driving unit, and means for drivingly connecting said driving unit to said pumping unit, said means including an elec t-rical insulating portion for electrically insulating the pumping unit from said driving unit.

4. The invention set forth in claim 3 with the addition that said driving unit includes means being adjustable during operation of the pump unit to vary the speed of the means for drivingly connecting the said driving unit to said pumping unit.

5. In apparatus for delivering an electrically conductive liquid to a liquid-utilizing device insulated from ground, a container for such liquid, a pump, electrically insulating supports for said container and pump, conduits for connecting said pump to said container and said device, an electric motor, and a driving connection between said motor and pump, said connection including an element of insulating material electrically insulating the pump from the motor.

6. The invention of claim 5 with the addition of a main base on which said motor is mounted and an atuxiliary base insulatingly supported from said main base and supporting said pump.

References Cited in the file of this patent UNITED STATES PATENTS 1,975,311 Creveling Oct. 2, 1934 1,983,825 Van Dam Dec. 11, 1934 2,036,810 Hurrell Apr. 7, 1936 2,100,359 Saeta Nov. 30, 1937 2,706,964 Ransburg et al. Apr. 26, 1955 2,724,581 Pahl et al. Nov. 22, 1955 2,728,689 Ransburg Dec. 27, 1955 2,781,279 Miller Feb. 12, 1957 2,849,155 Daley Aug. 26, 1958 2,873,889 Mori Feb. 17, 1959 

